1. Field of the Invention
ask The present invention relates to the field of micro-injecting devices and inkjet printheads, and more particularly, to membrane-containing micro-injecting devices. The present invention also relates to a method for manufacturing such micro-injecting devices.
2. Description of the Related Art
Generally, a micro-injecting device refers to a device which is designed to provide printing paper, a human body or motor vehicles with a predetermined amount of liquid, for example, ink, pharmaceutical liquid or petroleum using the method in which a predetermined amount of electric or thermal energy is applied to the abovementioned liquid, yielding a volumetric transformation of the liquid. This method allows the application of a small quantity of a liquid to a specific object.
Recently, developments in electrical and electronic technology have enabled rapid development of such micro-injecting devices. Thus, micro-injecting devices are being widely used in daily life. One example of the use of micro-injecting devices in daily life is the inkjet printer.
The inkjet printer is a form of micro-injecting device which differs from conventional dot printers in the capability of performing print jobs in various colors by using cartridges. Additional advantages of inkjet printers over dot printers are lower noise and enhanced quality of printing. For these reasons, inkjet printers are gaining immensely in popularity.
An inkjet printer generally includes a printer head having nozzles with a minute diameter. In such an inkjet printhead, the ink which is initially in the liquid state is transformed and expanded to a bubble state by turning on or off an electric signal applied from an external device. Then, the ink so bubbled is injected so as to perform a print job on a printing paper.
Examples of the construction and operation of several ink jet print heads of the conventional art are seen in the following U.S. Pat. U.S. Pat. No. 4,490,728, to Vaught et al., entitled Thermal Ink Jet Printer, describes a basic print head. U.S. Pat. No. 4,809,428, to Aden et aL, entitled Thin Film Device For An Ink Jet Printhead and Process For Manufacturing Same and U.S. Pat. No. 5,140,345, to Komuro, entitled Method Of Manufacturing a Substrate For A Liquid Jet Recording Head And Substrate Manufactured By The Method, describe manufacturing methods for inkjet printheads. U.S. Pat. No. 5,274,400, to Johnson et al, entitled Ink Path Geometry For High Temperature Operation Of Ink-Jet Printheads, describes altering the dimensions of the ink-jet feed channel to provide fluidic drag. U.S. Pat. No. 5,420,627, to Keefe et al, entitled Ink Jet Printhead, shows a particular printhead design.
In such a conventional inkjet printhead, a high temperature which is generated by a heating resistor layer is employed so as to eject ink. Here, if the ink contained in a liquid chamber is exposed to high temperature for a considerable time, thermal changes in the constituent parts of the ink may significantly reduce the lifespan of the device.
Recently, to overcome the above-mentioned problem, there has been proposed a method in which a substrate-shaped membrane is inserted between a heating resistor layer and a liquid chamber, and a transformation in volume of membrane is caused by the vapor pressure of a working liquid that fills a heating chamber. Thus, the ink contained in the liquid chamber is smoothly discharged.
In this case, direct contact between the ink and heating resistor layer can be avoided, since a membrane is inserted between the liquid chamber and the heating resistor layer. Thus, thermal changes in the ink can be minimized. An example of this type of printhead is seen in U.S. Pat. 4,480,259, to Kruger et at, entitled Ink Jet Printer With Bubble Driven Flexible Membrane.
In the above-described membrane-containing inkjet printhead, a membrane is expanded and contracted by a vapor pressure delivered from working liquid contained in a heating chamber, and is thus transformed in volume. Subsequently, an impact having a predetermined size is delivered to ink contained in a liquid chamber so that the ink can be ejected to external printing paper. Here, the above-described transformation in volume of the membrane occurs simultaneously all over the membrane.
Because the membrane is frequently transformed in volume during operation, if the membrane is made of nickel due to the impact delivery or operational resilience (that is, the restoring force to the original state) characteristics of nickel a weak part of the membrane may be In particular, this may occur in the portion of the membrane not supported by the structure of the heating chamber.
Moreover, the part which is not supported by the structure of the heating chamber, mentioned above, is a main operational part of the membrane which pushes ink upward. Therefore, if wrinkling occurs in such a main operational part, the mechanical characteristics of the membrane are significantly reduced.
On the other hand, if a membrane is made of polyimide, for example, in consideration of the stress or adhesion (to the heating chamber or liquid chamber) characteristics of this material, then the main operational part of the membrane is capable of remaining ductile and can endure deformation, for example, wrinkling, to some extent. However, the impact delivery characteristics and operational resilience are extremely weak for polyimide. Thus, the main part of the membrane cannot rapidly respond to generation of vapor pressure from the heating chamber, thereby disturbing the smooth operation of ink ejection.
Thus, the overall printing performance of the inkjet printhead is significantly lowered.